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    <style>
        div {
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            height: 300px;
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            padding: 0;
             border: 1px solid violet; 
        }

        ul {
            list-style: none;
            display: flex;
            flex-wrap: wrap;
        }
        li{
            opacity: 0.2;
             border: 1px solid hotpink; 
        }
        li:hover{
            opacity: 1;
        }

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<body>
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